My old iMac G3/400 (same model as yours I believe) ran with Panther and Tiger as well as OS9. I think I did a firmware update at one point, and regardless of whether you need it for a particular OS or not, it's best to keep the firmware up to date. But you may be out of luck with the mini disk, as it may only install to a PPC mini. If it includes a full installation of OS9, that should work, but Apple stopped doing that by the time I bought my PPC mini._________________Mini 1 (2012): 2.3 ghz Core i7; 10gb RAM, Corsair 240gb SSD, 500gb Seagate XT
Mini 2 (2009): 2.26 ghz Core 2 duo, 8gb RAM, 500gb SSD running Ubuntu
Also a 13" MacBook Air, 21.5" i5 iMac & 11.6" Acer 1810TZ running Ubuntu, openSUSE & Crunchbang

Good sleuthing, Aqua. I haven't used my own iMac G3/400 in years and I couldn't remember how I did all this. But the good news is once you've updated the firmware, you can run Tiger on it. As for Linux, I wasn't using it back when I was using the iMac G3.

I rather doubt that you need the firmware update to install Linux, and it's probably easier to just try the install than to go to the trouble of getting what you need to do the firmware if your version of OS9 doesn't work. With regard to Tiger, I'm quite sure that Apple was no longer providing OS9 as part of the package by that time.

What version of Linux would you put on the iMac? Your choices are a lot more limited than for the x86/amd64 architectures. I can vouch for Debian Lenny and openSUSE 11.0 on the G4; both provide Airport Extreme support and Mac-on-Linux works on them. But MOL is probably not of interest to you, and your iMac supports Airport, not Airport Extreme. You might even be interested in trying Yellow Dog, as it supports Airport better than Extreme._________________Mini 1 (2012): 2.3 ghz Core i7; 10gb RAM, Corsair 240gb SSD, 500gb Seagate XT
Mini 2 (2009): 2.26 ghz Core 2 duo, 8gb RAM, 500gb SSD running Ubuntu
Also a 13" MacBook Air, 21.5" i5 iMac & 11.6" Acer 1810TZ running Ubuntu, openSUSE & Crunchbang

Thanks guys. I will probably install Debian netinst for the minimum approach. Using x86 default kernel is a 486. Would that be the equivalent type of kernel for a G3? But first I will try a livecd to see how it work out.

I think OS9 came with my mini which had Panther also. I bought Tiger later on and it was only Tiger.

** UPDATE**
Good news and bad news...

The bad, I found the disc that came with the mini and it does include both OS9 & OSX, but they are not retail versions.

The good, I did find a PPC Ubuntu 4.10 disc I had ordered way back then. It should be a livecd also...I would always order x86, x86_64 and PPC discs.